I've found a way to set the default content for the text editor for all posts:
add_filter( 'default_content', 'my_editor_content' );
function my_editor_content( $str ) {
$str = "Enter <strong>description</strong> here.";
return $str;
};
However, I only want to use this filter for a custom post-type that I've created. Is there a way to register filters for only certain post-types?